1. Field of the Invention
The present invention relates generally to shoes that are put on at the time of daily outing, jogging or exercises, and more particularly to a shoe sole.
2. Description of the Related Art
Nowadays, typical jogging shoes comprise a midsole.
The midsole is arranged on top of an outer sole to absorb shocks upon landing. To this end, the midsole is made of a material such as resin sponge (foam) that is excellent in shock absorbing properties and resilience. In order to attain such properties, the hardness of the resin sponge is usually set to a relatively low value.
Any sports shoes provided with a midsole having such a low hardness are apt to undergo a drastic deformation at their arch portions upon walking and running, causing the user to experience fatigue. Thus, some recently developed shoes include a reinforcement device(s) fastened fixedly to the underside of the mid foot portion of the midsole to prevent possible deformations.
FIG. 8 is a bottom plan view of a shoe sole disclosed in Japan Utility Model Registration Pub. No. 2, 544, 047.
In this prior art, reinforcement devices 310 and 311 are disposed at a lateral side 10 and a medial side 11, respectively, of a shoe sole 300 so as to prevent any planar flexural deformations along the shoe sole face as well as to restrain arches of the arch of the foot from being depressed.
However, the arches of the arch portion are high at the medial side but low at the lateral side. For this reason, if the flexural rigidity of the reinforcement devices 310 and 311 is increased, then the low arch at the lateral side may be subjected to a thrust-up force, with the result that user may have a sense of incongruity.
Likewise, if the flexural rigidity of the reinforcement devices 310 and 311 are reduced, then the high arch at the medial side may be depressed and the user may feel fatigue, and the pronation of the inclining foot toward the medial side may be excessive.
FIG. 9 is a perspective view of a shoe sole disclosed in Japan Patent Laid-open Pub. No. Hei9-47305.
In this prior art, cup-like stabilizers 320 and 321 are disposed on top of a midsole 322. The stabilizers 320 and 321 are separately arranged at the lateral side 10 and the medial side 11, respectively, and have different hardness values. However, this prior art employs no structure for supporting the arches of the arch, and hence it can not prevent the medial side arch from being depressed.
FIG. 10 is a top plan view of a shoe sole disclosed in Japan Patent Laid-open Pub. No. Hei5-329005.
In this prior art, the medial side 331 of the rear foot portion and the medial side 332 of the arch portion of the outer sole of the shoe sole are designed to have a higher hardness than the remaining portion 333 of the outer sole. This prior art only addresses the hardness of the outer sole and does not contribute to preventing depression of the arches.
FIG. 11(a) is a top plan view of a midsole disclosed in Japan Patent Pub. No. Sho61-7801, and FIG. 11(b) is a side elevational view of the midsole disclosed in this publication.
This prior art discloses a pronation restricting member 202 disposed at the medial side 11 of the rear foot portion of the midsole 200, with the pronation restricting member 202 having a higher hardness than that of the midsole body 201. This prior art does not employ any structure to carry the arches of the arch and does not contribute preventing depression of the arches.
A midsole structure for enhancing the shock absorbing properties is disclosed in U.S. Pat. Nos. 4,372,058;4,741,114; and 5,079,856 and Japan Patent Laid-open Pub. No. Hei5-115306. In these prior art references, the midsole rear foot portion is provided with a concavity that is recessed upward from the bottom face of the midsole. The cross sectional area of the midsole is thus reduced due to the formation of the concavity. By virtue of this, the midsole rear foot portion readily compressively deforms, the deformation absorbing shock which occurs upon landing.
However, easy deformation of the midsole may result in a lowered stability of the shoe sole. For this reason, pronating action tends to become larger after the landing, namely, the action of the foot inclining toward the medial side after the landing brings about overpronation.
It is therefore a major object of the present invention to provide a shoe sole capable of achieving a suppressed pronation.
Another object of the present invention is to provide a shoe sole capable of realizing a suppression of planar flexural deformation, a suppression of thrust-up toward the lateral side arch and a suppression of depression of the medial side arch.
A further object of the present invention is to provide a shoe sole capable of fully absorbing shocks upon the landing.
According to a first aspect of the present invention, in order to attain the above objects, the shoe sole comprises an outer sole, a midsole and a reinforcement device made of resin plate.
The outer sole has a tread face and is divided into a forefoot portion and a rear foot portion. The midsole is formed on top of the outer sole over the forefoot portion, an arch portion, and the rear foot portion. The reinforcement device is fixed firmly to the bottom face of the arch portion of the midsole.
The reinforcement device is formed in an arch form at a medial side and a lateral side of a foot between the divided portions of the outer sole. In this aspect, hardness in a medial side portion of a foot of the reinforcement device is established to be higher than that in a lateral side portion of a foot of the reinforcement device. As a result of this, flexural rigidity in the medial side portion of the foot of the reinforcement device is established to be higher than that in the lateral side portion of the foot of the reinforcement device.
As used herein, xe2x80x9creinforcement device made of resin platexe2x80x9d refers to a plate-like or chip-like resin molded into a predetermined arch-shape, or a knit, fabric or paper molded integrally with resin.
xe2x80x9cMade of resin platexe2x80x9d means that the thickness of the reinforcement device is not so great, but it restricts by no means the geometry of the reinforcement device.
The reinforcement device is typically firmly secured to the underside of the arch portion of the midsole in an exposed manner, with the front and rear end portions of the reinforcement device being sandwiched between the midsole and the outer sole. However, the reinforcement device, except for the front and rear end portions, may partially or wholly be buried in the midsole as long as it is fixedly secured to the midsole in the vicinity of the underside of the midsole. The reinforcement device is thus firmly secured to the bottom surface side of the midsole, not to the top surface side.
In the present invention, xe2x80x9chardness of the reinforcement device made of resin plate is highxe2x80x9d means that Young""s modulus (modulus of longitudinal elasticity) of resin making up the reinforcement device is high. The reason this aspect is defined by the hardness is as follows. A higher Young""s modulus of a member leads generally to a higher flexural rigidity of the member. In the case of shoes available on the market, it is easier to measure the hardness of an element than to measure the Young""s modulus of members making up the reinforcement device. This is the reason that this aspect employs such a way of definition.
The hardness of the reinforcement device made of resin plate of the present invention can be measured by use of, e.g.,a JIS D-type hardness meter (hardness meter having a triangular pyramid-shaped penetrator).
A second aspect of the shoe sole of the present invention comprises an outer sole, a midsole and a reinforcement device made of resin plate. The outer sole has a tread face and is divided into a forefoot portion and a rear foot portion. The midsole is formed on top of the outer sole over the forefoot portion, an arch portion, and the rear foot portion. The reinforcement device is fixed firmly to the bottom face of the arch portion of the midsole.
The reinforcement device is formed in an arch form at a medial side and a lateral side of a foot between the divided portions of the outer sole. In this aspect, thickness in a medial side portion of a foot of the reinforcement device is established to be greater than that in a lateral side portion of a foot of the reinforcement device. As a consequence thereof, flexural rigidity in the medial side portion of the foot of the reinforcement device is established to be higher than that in the lateral side portion of the foot of the reinforcement device.
According to the present invention, due to the provision of the reinforcement device on both the foot medial side and lateral side, it is possible to fully suppress the planar flexure irrespective of the division of the outer sole into front and rear parts.
In particular, the present invention allows the flexural rigidity in the foot medial side portion of the reinforcement device to be higher than that in the foot lateral portion of the reinforcement device, whereby the user is less likely to have a thrust-up feeling in the lateral side arch of the arch and it is possible to restrain the foot medial side arch of the arch from being depressed to thereby relieve the fatigue which the foot may experience.
In addition, the medial side arch of the arch has less of a tendency to be depressed in this manner so that the foot is restrained from being inclined toward the medial side, thereby enabling pronation to be suppressed.
It will be appreciated that by establishing the flexural rigidity of the reinforcement device by the resin hardness, the thickness of the reinforcement device can be set to an appropriate small value so that the lightweight properties of the shoe sole are not impaired.
In a preferred embodiment of the present invention, the reinforcement device is divided into two parts, one in a medial direction and the other in a lateral direction of a foot. Such a division into two parts permits the reinforcement device to be notched at the central site of the arch, thereby reducing the weight of the reinforcement device.
In the present invention, preferably the reinforcement device has a diagonal reinforcement portion arranged almost in the center between the medial and lateral sides of the foot. The diagonal reinforcement portion has an inclination extending in a diagonally outward direction from the rear end of the forefoot portion of the outer sole to the front end of the rear foot portion of the outer sole.
The foot is subjected to a pronation when the heel lateral side is inclined toward the toe medial side. As measures against this, the diagonal reinforcement device serves to enhance the flexural rigidity so as to restrain the foot from being inclined. A further suppression of pronation is thus achieved.
In another preferred embodiment of the present invention, if the midsole is made of foam resin, then the medial side of the arch portion of the midsole is established to have a higher hardness value than that of the lateral side of the rear foot portion of the midsole and the forefoot portion of the midsole.
By establishing the hardness of the midsole in this manner, the medial side of the arch portion of the midsole is subjected to a reduced compressive deformation and to a reduced compression set. The coaction with the reinforcement device provides a support to the medial side of the midsole causing a further suppression of the depression of the medial side arch of the arch. Moreover, the support of the midsole by the hard reinforcement device can suppress the depression of the arch without increasing the midsole hardness to a large extent so that the user does not have a sense of incongruity at the medial side arch of the arch.
According to a third aspect of the present invention, the shoe sole comprises an outer sole and a midsole.
The outer sole has a tread face in a forefoot portion and a rear foot portion. The midsole is formed extending from a forefoot portion to a rear foot portion on top of the outer sole.
The rear foot portion of the midsole is formed extending from a medial side to a lateral side of a foot. An exposed portion, that is not covered with the outer sole, is arranged almost in the center between the medial and lateral sides of the foot in the rear foot portion of the midsole.
The exposed portion has a hollow concavity formed upwardly from the tread face (bottom face). The concavity has a rootbottom portion of which depth is the largest in cross section of the midsole.
The rootbottom portion of the concavity is elongated along substantially the longitudinal direction of the shoe sole. The rootbottom portion of the concavity is arranged at a site closer to the lateral side of the foot. The concavity becomes gradually deeper as it is closer from the medial side of the foot to the rootbottom portion. As a result of imparting such a geometry to the concavity, in the rear foot portion of the midsole, the lateral side is easy to deform compressively as compared with the medial side.
Description will then be made of the principle and effect of this aspect.
Upon walking and running, the majority of human beings land on the lateral side of the rear foot portion of the foot. At the time of this landing, the lateral side of the rear foot portion of the foot is subjected to the greatest shock load. It is therefore necessary to relieve the shock load exerted on the lateral side of the rear foot portion of the foot.
In this aspect, the midsole rear foot portion is formed with the concavity that is recessed upward from the bottom face and of which rootbottom portion is offset toward the foot lateral side. For this reason, the lateral side of the midsole rear foot portion can have a reduced pressure-receive area as compared with the medial side of the midsole rear foot portion, so as to be easily compressively deformed. As a result of this, the lateral side of the midsole rear foot portion can compressively deform upon the landing to a large extent, contributing to enhanced shock absorbing properties at the time of the landing.
After the landing, on the contrary, the majority of human beings have a pronating action wherein the foot is slightly inclined toward the medial side.
In the present invention, the rootbottom portion of the concavity is arranged at a site closer to the lateral side of the foot. This allows the medial side of the midsole rear foot portion to have a larger pressure-receive area and thus to present a higher resistance to the compressive deformation than the lateral side of the midsole rear foot portion. As a result of this, the medial side of the midsole rear foot portion is incapable of large compressive deformation after the landing, thus suppressing the pronating action and eliminating any possibilities of occurrence of overpronation.
In the present invention, the sectional geometry of the concavity formed in the midsole is structured to achieve improved shock absorbing property and a suppressed pronating action, thereby preventing the geometry of the midsole from becoming complicated.
In a preferred embodiment of the present invention, the rear foot portion of the outer sole is formed substantially into a shape of horseshoe.
Such a horseshoe-shaped outer sole adds to stability upon the landing.
In another preferred embodiment of the present invention, the midsole is made of a foam resin and the medial side of the rear foot portion and the medial side of the arch portion of the midsole are established to have a higher hardness value than that of the lateral side of rear foot portion and the forefoot portion of the midsole.
Such an establishment of the hardness of the midsole helps the lateral side of the midsole rear foot portion to easily compressively deform. On the other hand, the medial side of the midsole rear foot portion and the medial side of the arch portion become less liable to compressively deform. The shock absorbing effect and the pronation suppressing effect can thus be enhanced.
According to a fourth aspect of the present invention, the shoe sole comprises an outer sole, a midsole and a reinforcement device made of resin plate. The outer sole has a tread face and is divided into a forefoot portion and a rear foot portion. The midsole is formed on top of the outer sole over the forefoot portion, an arch portion, and the rear foot portion. The reinforcement device is fixed firmly to the bottom face of the arch portion of the midsole.
The rear foot portion of the midsole is formed extending from a medial side to a lateral side of a foot, An exposed portion, that is not covered with the outer sole, is arranged almost in the center between the medial and lateral sides of the foot in the rear foot portion of the midsole.
The exposed portion has a hollow concavity formed upwardly from the tread face (bottom face). The concavity has a rootbottom portion of which depth is the largest in cross section of the midsole.
The rootbottom portion of the concavity is elongated along substantially the longitudinal direction of the shoe sole. The rootbottom portion of the concavity is arranged at a portion closer to the lateral side of the foot, wherein.
The concavity becomes gradually deeper as it is closer from the medial side of the foot to the rootbottom portion. By shaping the concavity in this manner, the midsole rear foot portion can easily compressively deform in the lateral side than in the medial side.
The reinforcement device is formed in an arch form at the medial side and the lateral side of the foot between the divided portions of the outer sole, In this aspect, flexural rigidity in the medial side portion of the foot of the reinforcement device is established to be higher than that in the lateral side portion of the foot of the reinforcement device.